Abstract

Corals exposed to high light intensity may be susceptible to bleaching, therefore understanding the effect of light on coral photophysiology is vital to their protection. Goniastrea corals collected from Hall Bank Reef were placed under four different light filter treatments: blue, clear, red and UV opaque under outdoor conditions at Perth, Western Australia and photosynthetic activities were measured using a Diving-PAM. The main aim of this study was determining light composition (exposed λ) effect on the corals’ photosynthetic efficiency and survival rate. The photosynthetic efficiency was quantified as Fv/Fm (the effective quantum yield of Photosystem II), the electron transport rate (ETR and ETRmax), non-photochemical quenching (NPQ), and alpha (α). Coral survival was monitored until all corals had died, and it was found that corals subjected to shorter wavelengths (the blue light treatment) survived longer than other light treatments. The corals were initially collected from 12 m depth, where they are naturally adapted to an environment that is exposed to mainly blue light (450-495 nm); therefore they would be adapted to these conditions. The Fv/Fm dropped significantly over the course of the experiment, with higher Fv/Fm reduction in clear and UV light filter treatments when compared to corals kept at blue and red spectra. Fv/Fm reduction over time may be due to chronic photoinhibition damaging PSII and lowering the overall photosynthetic yield of the algal symbiont. The Fv/Fm of the corals subjected to the blue light treatment was consistently higher, most likely due to lower PAR (Photosynthetically Active Radiation) level transmitting this filter. The diurnal trials indicated there was a peak in Fv/Fm at 9am, before decreasing at midday under all light treatments. This was attributed to the high irradiance at this time of day causing dynamic photoinhibition and thus a temporary lowering of the photosynthetic yield of the symbionts. ETRmax, α and NPQ did not change significantly over time, however α and ETRmax showed a general trend of increasing until midday (when irradiance is highest) and then decreasing. Overall this showed that corals exposed to broader bands of the electromagnetic spectrum are more likely to experience damage to PSII and subsequent decrease in photosynthetic yield, as well as lowered survival rate. The results of this study indicate that altering the transmission of light in the ocean may have detrimental effects on coral reefs.